BACILLUS AEROGENES CAPSULATUS. 465 



the stain. The specimen is then examined in the color- 

 ing-solution, after soaking up the excess with filter paper, 

 the thin layer of coloring fluid not interfering with a clear 

 view of the bacteria and their capsules. After mounting 

 in Canada balsam the capsules are not nearly so distinct. 

 The width of the capsule varies from one-half to twice 

 the thickness of the bacillus. Its outer margin is stained, 

 leaving a clear zone immediately around the bacillus. 



It was at first thought that the bacillus produced no 

 spores, but Dunham 1 found that spores were produced 

 upon blood-serum, and especially upon LofHer's blood- 

 serum bouillon mixture. The spores resist desiccation 

 and exposure to the air for ten months. They stain 

 readily in hot solutions of fnchsin in anilin water, and 

 are not decolorized by a moderate exposure to the action 

 of 3 per cent, solution of hydrochloric acid in absolute 

 alcohol. They are oval, -and are usually situated near 

 the middle of the bacillus, which is distended because of 

 the large size of the spore and bulges at the sides. 



The bacillus is anaerobic. It grows upon all culture- 

 media, both at the room-temperature and at the tempera- 

 ture of incubation, best at the latter. The bacillus grows 

 in ordinary neutral or alkaline gelatin, but better in gela- 

 tin containing glucose, in which the characteristic gas- 

 production is marked. Soft gelatin, made with 5 instead 

 of 10 per cent, of the crude gelatin, is said to be better 

 than the ordinary medium. 



There is no distinct liquefaction, but in 5 per cent, 

 gelatin there is sometimes a softening that can be best 

 demonstrated by tilting the tube and observing that the 

 gas-bubbles change their position, as well as by noticing 

 that the growth tends to sediment. 



In making agar-agar cultures careful anaerobic precau- 

 tions must be observed. The tubes should contain con- 

 siderable of the medium, which should be boiled and 

 freshly solidified before using. The implantation should 

 be deeply made with a long wire. The growth takes 



1 Bull, of the Johns Hopkins Hospital, April, 1897, p. 68. 

 30 



